X-ray opaque esters or amides of iodosubstituted benzoic acid according to formula I and polymers and dental materials produced therefrom. ##STR1## R.sup.1 =hydrogen or C.sub.1 to C.sub.3 alkyl, preferably H or CH.sub.3 ; R.sup.2 =straight-chain or branched C.sub.1 to C.sub.6 alkylene, oxyalkylene or arylene, preferably C.sub.2 to C.sub.4 alkylene and particularly preferably --CH.sub.2 --CH.sub.2 -- and --CH.sub.2 CH(--)CH.sub.2 --; X=O or NH, preferably O; R.sup.3 -R.sup.7 =at least 3 iodine substituents, preferably in R.sup.3, R.sup.4 and R.sup.6 or R.sup.3, R.sup.5 and R.sup.7 position, the other groups are hydrogen, C.sub.1 to C.sub.6 alkyl, C.sub.1 to C.sub.6 alkoxy, --Cl, --Br, --OH, --NH.sub.2, --N(C.sub.1 to C.sub.6 alkyl).sub.2 or --NH--CO--(C.sub.1 to C.sub.6 alkyl), preferably R.sup.3, R.sup.4, and R.sup.6 are=I and R.sup.5 and R.sup.7 =H, or R.sup.3, R.sup.5 and R.sup.7 =I and R.sup.4 and R.sup.6 =--NH(COCH.sub.3); n=1, 2 or 3, preferably 1 or 2. The benzoic acid esters and amides according to the invention can be well polymerized radically or anionically, the polymers are well soluble in the usual dental monomers. Dental materials produced from the monomers or polymers are characterized in that the X-ray opaque component is bonded covalently into the polymeric matrix material and cannot therefore be washed out. Furthermore, excellent X-ray opacity can be achieved without using fillers.